The Fiery Debut of the Full Cat Rocket (Half Cat Rocketry)

May 20, 2023
Half Cat Rocketry's latest and biggest rocket, rivalling most University liquid rocket teams in thrust and impulse, underwent it's first flight configuration test campaign. The Half Cat folks were the first to successfully launch and recover a liquid rocket as part of the DPF challenge, using their original Half Cat rocket. Since then, they have championed nitrous alcohol bipropellants for amateur and student rocketry, offering plans and calculators for anyone to use.
The Full Cat rocket represents the largest application of nitrous alcohol in their lineup of rocket designs, and makes use of much of the hardware they've tested on other rockets, such as their pyrotechnic valves. This first test was also the first use of the iconic large vertical test stand at FAR since the days of CALVEIN/GSC. The rocket was secured at the top with a suspended bracket, and secured to the sides with steel braided stay cables.
This first static test did not perform as expected, with a burst fuel line spraying alcohol out the sides, creating a flashy fireball while the nitrous ejects out the nozzle. This was later attributed to inadequacy of compression fittings for nylon tubing, and was swapped out for push-to-connect fittings for their next test, which is to be featured on this channel in the future. Nitrous Oxide is often noted to be more difficult to ignite than pure oxygen, which may have helped limit the damage done by the two propellants ejecting in atmosphere. Though it appears catastrophic, it was just a fuel air deflagration and a liquid nitrous stream, and damage to the vehicle was superficial. Half Cat Rockets rarely seem to fail in a destructive manner, which makes this an appropriate baptism of fire for Full Cat.
The test campaign had to be suspended because this fire propagated upwards towards the one corner of the stand which contained the battery, and burnt it up. In more recent tests, the battery is housed in a protected container, among other procedural changes.

[@Thorgon-Cross]

A compression fitting to hold a nylon hose on in a pressurized system...... even in pluming that is a "no no" because it can not hold much pressure. I get using off the shelf parts and lightest system but it does not matter how much money or weight you are saving if it does not work. While "shark-bite" type push-to-connect fittings do have greater hold strength they are prone to leaking under pressure without full failure. If dead set on using soft line, (why? when are lines are easy) crimped on threaded end like those used on stainless steel braided lines are the best bet...on that though you can buy such lines pre-made and rated for over 300+psi...

[@DerekHonkawa]

I think the Half Cat guys may have come to that conclusion with compression, and the leaking of push-to-connect fittings may not be as significant a risk with nitrous being tougher to light and the use of alcohol instead of kerosene. I am interested to see how far they can push these soft lines, since rigid metal tubing brings about its own headaches and difficulties and needs a wider array of tools and cleanings. Using what they use, Half Cat can refit their rocket in the field. Whether or not these benefits necessitate more frequent refitting requires a larger sample size.